Film grain, gate weave and flicker, explained
Film is a strip of plastic coated with silver salts and pulled through a machine by a claw. Every part of that sentence shows up on the screen.
The emulsion
A film emulsion is gelatin with tiny crystals of silver halide suspended in it. Light changes the crystals it hits, and the developer turns those crystals into specks of black metallic silver. A black-and-white picture is nothing more than where the silver ended up. Color film adds layers of dye that form alongside the silver, and then the silver is bleached away.
The crystals were never all the same size, and they never sat in a neat grid. That randomness is the start of everything on this page.
Orthochromatic and panchromatic
Early emulsions saw blue and green light but were nearly blind to red. Photographers called them orthochromatic. On orthochromatic film a red rose comes out almost black, lips darken, freckles stand out, and a blue sky burns to plain white. Actors and sitters wore heavy, pale make-up to fight it, which is part of why faces in early films look so pale and hard.
Panchromatic film, sensitive to the whole visible spectrum, existed early on but was slower and dearer. It took over motion pictures in the 1920s, and by the end of that decade it was the norm. Skin tones softened, skies kept some grey, and red stopped looking like a shadow.
On the dial, the 1890s and 1900s are mostly orthochromatic. The 1920s give you both: compare 16 mm Home Cine with Panchromatic 16mm on a face, or on anything red.
Grain
Grain is the silver crystals made visible. You see it most in smooth mid-tones: a sky, a wall, a cheek. Two things decide how much you see.
- Speed. A faster film, one that needs less light, uses larger crystals. Low-light and high-speed looks are grainier.
- Gauge. The same grain is enlarged more when the frame is small. An 8 mm frame is projected many times larger than a 35 mm frame on the same screen, so its grain looks coarser.
The app sizes its grain by gauge: coarse for 8 mm and Super 8, finer for 16 mm, finest for 35 mm. The grain is redrawn on every frame, because on real film every frame has its own crystals. That shimmer is a large part of why film looks alive. Video and digital looks use sensor noise instead, which is finer and tied to individual pixels.
Halation
Bright light doesn't stop in the emulsion. Some of it passes through, reflects off the back of the film base and comes back up, exposing the emulsion a second time around the highlight. The result is a soft glow around lamps, windows and sunlit edges. Later films added an anti-halation backing to absorb that light, and the glow faded from the picture.
The app adds halation in the optics stage, before the grain. It picks out the brightest parts of the frame, spreads them and lays them back over the picture, so the glow is soft while the grain on top of it stays sharp. The film decades, from the 1890s to the 1970s, carry it most.
Gate weave
A movie camera pulls the film down one frame at a time with a claw, holds it still in the gate for the exposure, then pulls again. The claw and the sprocket holes were never perfect, and the film itself could shrink or curl. Each frame landed a fraction of a millimeter away from the last. On screen the whole picture drifts and sways very slightly, as if the image were floating.
The app moves the whole frame by a small amount, slowly, mostly up and down, with a margin cropped off so the edges never show. It is subtle on purpose: real weave is felt more than seen, until a title card or a horizon makes it obvious.
Flicker
Old film brightens and darkens from one frame to the next. There are several real causes. A hand-cranked camera exposed each frame for a slightly different time as the crank speed changed. Shutters weren't always consistent, and early processing varied across a reel. Projection added its own pulse from the lamp and the shutter.
The app changes the brightness of each frame by a random amount, all three colors together, so a grey stays grey. Some looks also have a slow exposure drift on top, the way a camera's exposure wandered as clouds passed and nobody adjusted the aperture.
Tinting and toning
Silent films were rarely shown in plain black and white. Two cheap ways to add color were common, and they look different.
- Tinting dyed the whole film, so the light parts of the picture took the color and the blacks stayed black. Conventions varied, but blue often meant night, amber meant lamplight or interiors, and red meant fire.
- Toning chemically replaced the silver with a colored compound, so the dark parts took the color and the highlights stayed clear. A sepia-toned shot has brown shadows and white highlights.
The app does both after the color response, so a red object first goes dark the way it did on the emulsion, and then takes the tint or the tone. Hand-colored and stencil-colored technologies go further. Stencil Colour Film in the 1900s lays flat patches of color that spill over the outlines, the way color applied through cut stencils did. Hand-Coloured Film in the 1890s washes soft, pale color over the grey picture, as if it had been brushed on.
Early color processes
Before full color film, inventors tried to get color from two colors instead of three. A two-color additive process photographed alternate frames through red and green filters. It shows fringes of color on anything that moves, because the two colors were never captured at the same instant. A two-color subtractive process printed a cyan and a red image together, which is why its skies tend towards turquoise and its skin towards pink. A lenticular process put tiny lenses into the film base and gave soft, muted color with a fine line structure. You will find them in the 1910s and 1920s. Three-strip color, with its deep, saturated dyes, arrives in the 1930s.
Damage
Film is a physical thing that gets handled. Every pass through a projector risked a scratch, dust settled on it, and splices and dirt built up. A scratch on a projected print runs vertically, because it was dragged along the strip, and it jumps a little from frame to frame.
The app draws scratches and dust in the last stage, on top of everything, and draws new ones on each frame. Most technologies come from the lab clean. The ones with heavy damage are named for it: Early Film Print, Aged Film Copy, Faded Color Archive, Aged Super 8 Archive.
DEGREE scales damage like any other defect, but it never adds damage to a look that has none. At DEGREE 12 a clean reel gets heavier grain, flicker and weave, not scratches. More on that in DEGREE.